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Instructor: Prof. Andrey Korytov, Prof. Paul Avery
PHYSICS DEPARTMENT
PHY 2054
Final Exam
December 13, 2014
Signature:
Name (PRINT, last, first):
On my honor, I have neither given nor received unauthorized aid on this examination.
YOUR TEST NUMBER IS THE 5-DIGIT NUMBER AT THE TOP OF EACH PAGE.
DIRECTIONS
(1) Code your test number on your answer sheet (use 76–80 for the 5-digit number). Code your name on your
answer sheet. DARKEN CIRCLES COMPLETELY. Code your student number on your answer sheet.
(2) Print your name on this sheet and sign it also.
(3) Do all scratch work anywhere on this exam that you like. At the end of the test, this exam printout is to be turned in.
No credit will be given without both answer sheet and printout with scratch work most questions demand.
(4) Blacken the circle of your intended answer completely, using a #2 pencil or blue or black ink. Do not
make any stray marks or the answer sheet may not read properly.
(5) The answers are rounded off. Choose the closest to exact. There is no penalty for guessing.
>>>>>>>>WHEN YOU FINISH <<<<<<<<
Hand in the answer sheet separately.
Constants
−12
−31
ǫ0 = 8.85 × 10
F/m me = 9.11 × 10
kg
mp = mn = 1.67 × 10−27 kg e = 1.6 × 10−19 C
k = 9 × 109 N m2 /C2 µ0 = 12.56 × 10−7 H/m NA = 6.02 × 1023 atoms/mole c = 3 × 108 m/s
nH2 O = 1.333
micro = 10−6
nano = 10−9
pico = 10−12
1. An electron with velocity v0 = 2×107m/s along the +x direction enters a region with a uniform electric field of magnitude
5000 V/m in the −y direction. If the electron travels 5.0 cm in the x direction, what is the deflection in the y direction
(in cm)?
(1) +0.27
(2) −0.16
(3) +0.54
(4) −0.54
(5) +0.81
2. Four charges of magnitude Q (but different signs, as in the figure) are arranged on the corners
of a square of side 25 cm. Calculate Q (in µC) if the potential energy of the system of the four
charges is −1.5 J.
(1) 4.0
(2) 2.8
(3) 3.2
(4) 6.0
+Q
-Q
-Q
+Q
(5) 7.5
3. In the circuit shown find the charge (in µC) on C5 . The values are C1 = 5 µF, C2 = 3 µF,
C3 = 5 µF, C4 = 2 µF, C5 = 4 µF, and V = 15 V.
C2
V
C1
C4
C5
C3
(1) 14.3
(2) 96.4
(3) 21.4
(4) 7.2
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4. A 14.0 g conducting rod of length 1.30 m and resistance 8.0 Ω slides freely downward between two
vertical conducting rails without friction. The entire apparatus is placed in a uniform magnetic
field B. Ignore the electrical resistance of the rails. Calculate B if the terminal velocity of the
rod is 2.5 m/s. (g = 9.8 m/s2 )
(5) 10.1
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0.51 T
1.6 T
0.26 T
0.73 T
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(1)
(2)
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5. Four long parallel wires pass through the corners of a square with side 15 cm and currents I
and 2I as shown in the figure. Calculate I if the magnitude of the magnetic field at the center
of the square is 40 µT.
(1) 5.0 A
(2) 7.5 A
(3) 10 A
(4) 3.5 A
6. In the circuit shown in the figure, the switch is in position 1 for a long time. It is then
moved to position 2. How long will it take for the current through R2 to reach 1.0 A
after the switch is moved to its new position? The values are C = 20 µF, R1 = 5 kΩ
and R2 = 5 Ω. The battery has an emf of 40 V.
I
I
2I
2I
(5) 2.5 A
1 2
+
C
R2
R1
(1) 0.21 ms
(2) 0.34 ms
(3) 1.00 ms
(4) 0.73 ms
(5) 0.42 ms
7. A coil with an inductance of 0.25 H and a resistance of 33 Ω is connected to a 10 V battery. Find the current in the
circuit after the coil has been connected for 2.5 ms.
(1) 0.085 A
(2) 0.218 A
(3) 0.021 A
(4) 0.137 A
(5) 0.176 A
8. An alpha particle consists of two protons and two neutrons (proton and neutron masses are approximately equal). The
alpha particle is projected head-on toward a very heavy point particle of charge Q at an initial velocity 1.5 × 107 m/s
from a distance 75 fm (1 fm = 10−15 m). The alpha particle reaches a distance of 49 fm from the heavy particle before
turning around. Find the charge Q.
(1) 3.7 × 10−17 C
(2) 1.3 × 10−17 C
(3) 7.4 × 10−17 C
(4) 2.0 × 10−17 C
(5) 6.7 × 10−17 C
9. A silver wire of diameter 1.0 mm carriers a current I. The number density of conduction electrons in silver is 8.47 ×
1028 m−3 . If it takes 10 min (on average) for a conduction electron to move 2.0 cm along the wire, find the current I.
(1) 355 mA
(2) 235 mA
(3) 585 mA
(4) 825 mA
(5) 195 mA
10. Two Styrofoam balls with the same mass m = 9.0 × 10−8 kg and the same positive charge Q are suspended from the
same point by insulating threads of length L = 0.5 m. At equilibrium, the separation of the balls is 3.0 cm. What is the
charge Q (in nC)?
(1) 0.051
(2) 0.018
(3) 0.037
(4) 0.076
(5) 0.107
11. A laser beam of wavelength 420 nm has intensity 10 W/m2 . The amplitudes of the associated electric and magnetic
fields, in V/m and µT, are, respectively
(1) 87, 0.29
(2) 61, 0.20
(3) 123, 0.41
(4) 43, 0.14
(5) 31, 0.10
12. A horizontal beam of unpolarized light is incident on a stack of 4 polarizing sheets arranged perpendicular to the beam.
The axes of polarization of the sheets, in order, are oriented at angles 0◦ , 60◦ , 30◦ , and 90◦ with respect to the vertical,
measured clockwise around the beam direction. What is the approximate intensity of the beam emerging from the stack
relative to the initial intensity?
(1) 2%
(2) 20%
(3) 0%
(4) 5%
(5) 40%
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13. A remote galaxy moves away from us with a velocity equal to 1/5 of the speed of light. A civilization leaving in that
galaxy transmits a SOS signal at a frequency of 100 MHz. At what frequency here on Earth would one detect the signal?
(1) 82 MHz
(2) 122 MHz
(3) 67 MHz
(4) 150 MHz
(5) 73 MHz
14. Flat sheets of two materials, the first of index of refraction 1.63 and thickness 2 mm, and the second of index of refraction
1.52 and thickness 3 mm, are placed on top of one another with no air gap between them. A point source of light is
placed just below the bottom surface of the second material. What is the radius of the circle of light that emerges from
the top of the first material?
(1) 4.2 mm
(2) 5.3 mm
(3) 3.2 mm
(4) 3.9 mm
(5) 3.4 mm
15. Two identical converging lenses each of focal length 1 m are placed 1 m apart. What is the overall magnification of the
two-lens system for an object placed 50 cm away from the front lens?
(1) −2
(2) −1
(3) +1
(4) +2
(5) +0.5
16. A person takes a picture of the moon using a film camera, using its normal lens of 50 mm focal length. Assuming the
moon’s diameter to be approximately 3,600 km and its distance from the earth as 384,000 km, what is the approximate
diameter of the moon’s image on the film?
(1) 0.5 mm
(2) 50 mm
(3) 0.2 mm
(4) 25 mm
(5) 0.25 mm
17. A nearsighted person can see clearly only objects at distances between 18 cm and 60 cm of her eye. To see distant
objects, she should wear eyeglasses of what prescription in diopters?
(1) −1.67
(2) −1.56
(3) −2.33
(4) −5.56
(5) −0.60
18. Coherent light of wavelength 500 nm illuminates two slits that are separated by 0.1 cm. The separation between adjacent
bright fringes on a screen 5 m from the slits is:
(1) 0.25 cm
(2) 0.10 cm
(3) 0.50 cm
(4) 1.0 cm
(5) 0.05 cm
19. Two light waves travel in air with wavelength 520 nm, and they are initially in phase. Each passes through a block of
length L before passing back into the air. One travels through glass with index of refraction n1 = 1.65, and the other
passes through ice with index of refraction n2 = 1.31. What is the minimum value of L for which the waves will undergo
full destructive interference?
(1) 765 nm
(2) 2400 nm
(3) 4800 nm
(4) 400 nm
(5) 1260 nm
20. White light reflected at perpendicular incidence from a uniform soap film (n = 1.4) suspended in air has an interference
maximum at 600 nm and a minimum at 525 nm, with no minima between 600 nm and 525 nm. What is the film thickness
(in nm)?
(1) 750
(2) 1050
(3) 250
(4) 420
(5) 75